Air gap process

ABSTRACT

Methods are described for forming “air gaps” between adjacent metal lines on patterned substrates. The common name “air gap” will be used interchangeably with the more technically accurate “gas pocket” and both reflect a variety of pressures and elemental ratios. The air gaps are produced within narrow gaps between copper lines while wide gaps retain dielectric material. Retention of the dielectric material within the wide gaps enables formation of a desirable planar top surface. Using a hardmask layer and a selective dry-etch process enables a wet processing step to be avoided right before the formation of the air gaps. The air gaps can have a dielectric constant approaching one, favorably reducing interconnect capacitance compared with typical low-k dielectric materials.

FIELD

Embodiments of the invention relate to formation of air gaps betweencopper lines.

BACKGROUND

Semiconductor device geometries have dramatically decreased in sizesince their introduction several decades ago. Modern semiconductorfabrication equipment is routinely used to produce devices havinggeometries as small as 28 nm and less, and new equipment designs arecontinually being developed and implemented to produce devices with evensmaller geometries. As device geometries decrease, the impact ofinterconnect capacitance on device performance increases. To reduceinterconnect capacitance, inter-layer materials that have traditionallybeen formed of silicon oxide are being formed using lower dielectricconstant materials (low k materials). Some low k materials that havebeen used include fluorinated silicon oxide, carbonated silicon oxide,and various polymers and aerogels. While these and other low k materialshave been used successfully in the manufacture many different types ofintegrated circuits, new and improved processes that can create regionsof low dielectric constant material between adjacent metal lines onsubstrates are desirable.

Copper lines are desirable because of their low resistivity. Usingcopper lines decreases signal loss but also raises the maximum frequencyof operation for integrated circuits. The signal delay is proportionalto the resistance of the copper lines times the capacitance betweencopper lines. However, it has been difficult to reduce the capacitanceof the interlayer insulating layer used with copper interconnects due toprocess sequence integration issues.

Methods are needed to form gas pockets (generally referred to as airgaps) between low-resistivity metal (e.g. copper) lines in integratedcircuits.

SUMMARY

Methods are described for forming “air gaps” between adjacent metallines on patterned substrates. The common name “air gap” will be usedinterchangeably with the more technically accurate “gas pocket” and bothreflect a variety of pressures and elemental ratios. The air gaps areproduced within narrow gaps between copper lines while wide gaps retaindielectric material. Retention of the dielectric material within thewide gaps enables formation of a desirable planar top surface. Using ahardmask layer and a selective dry-etch process enables a wet processingstep to be avoided right before the formation of the air gaps. The airgaps can have a dielectric constant approaching one, favorably reducinginterconnect capacitance compared with typical low-k dielectricmaterials.

Embodiments of the invention include methods of forming air gaps betweenconducting lines. The methods include forming and patterning a hardmasklayer on a patterned substrate. The patterned hard mask layer does notcover dielectric material in a narrow gap between two adjacentconducting lines but does cover dielectric material in a wide gapbetween two other adjacent conducting lines. The methods further includeflowing a pretreatment gas into a substrate processing region housingthe patterned substrate while forming a local plasma in the substrateprocessing region to treat the dielectric in the narrow gap. The methodsfurther include flowing a fluorine-containing precursor into a remoteplasma region separated from the substrate processing region by ashowerhead while forming a remote plasma in the remote plasma region toform plasma effluents. The methods further include flowing the plasmaeffluents into the substrate processing region to etch the dielectricmaterial from the narrow gap while retaining the dielectric material inthe wide gap. The methods further include forming a non-conformal layerof dielectric on the patterned substrate. Dielectric formed on eachconducting line grow and join together to trap an air gap in the narrowgap while the wide gap remains filled with dielectric material. Thenon-conformal layer of dielectric may comprise silicon oxide or apreferably a low-k dielectric (e.g. SiOC or SiOCH) in embodiments.

Embodiments of the invention include methods of forming air gaps betweencopper lines on a patterned substrate. The methods include patterning alow-k dielectric layer on the patterned substrate. The methods furtherinclude depositing copper on the patterned low-k dielectric layer. Themethods further include planarizing the copper to expose a narrow gapbetween two adjacent copper lines and a wide gap between two otheradjacent copper lines. The methods further include forming andpatterning a hardmask layer, wherein the patterned hard mask layercovers low-k material in the wide gap but does not cover low-k materialin the narrow gap. The methods further include flowing a pretreatmentgas into a substrate processing region housing the patterned substratewhile forming a local plasma in the substrate processing region to treatthe low-k material in the narrow gap. The methods further includeflowing NF₃ into a remote plasma region separated from the substrateprocessing region by a showerhead while forming a remote plasma in theremote plasma region to form plasma effluents. The methods furtherinclude flowing the plasma effluents into the substrate processingregion to etch the low-k material from the narrow gap while retainingthe low-k material in the wide gap. The methods further include forminga non-conformal layer of dielectric on the patterned substrate.Dielectric formed on each copper line grow and join together to trap anair gap in the narrow gap while the wide gap remains filled with low-kdielectric material.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the embodiments. The features and advantagesof the embodiments may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the embodimentsmay be realized by reference to the remaining portions of thespecification and the drawings.

FIG. 1 is a flow chart of an air gap process according to embodiments.

FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G and 2H are cross-sectional views of apatterned substrate during an air gap process according to embodiments.

FIG. 3A shows a substrate processing chamber according to embodiments.

FIG. 3B shows a showerhead of a substrate processing chamber accordingto embodiments.

FIG. 4 shows a substrate processing system according to embodiments.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

Methods are described for forming “air gaps” between adjacent metallines on patterned substrates. The common name “air gap” will be usedinterchangeably with the more technically accurate “gas pocket” and bothreflect a variety of pressures and elemental ratios. The air gaps areproduced within narrow gaps between copper lines while wide gaps retaindielectric material. Retention of the dielectric material within thewide gaps enables formation of a desirable planar top surface. Using ahardmask layer and a selective dry-etch process enables a wet processingstep to be avoided right before the formation of the air gaps. The airgaps can have a dielectric constant approaching one, favorably reducinginterconnect capacitance compared with typical low-k dielectricmaterials.

One way to form metal lines involves depositing metal into trenches andgaps in a patterned dielectric layer such as silicon oxide or a low-kdielectric. This techniques is referred to as metal damascene owing toits similarity to ancient decorative processes. Chemical mechanicalpolishing may be used to remove the copper located above the patterneddielectric layer. Air gaps may then be formed in between copper lines byetching away the patterned dielectric material and then forming anon-conformal dielectric layer which pinches off air gaps in narrowgaps. However, most layers have wide gaps in addition to narrow gaps andthe wide gaps do not pinch off so no air gap is formed. The narrow gapsmay exhibit air gaps while the wide gaps form a depression which meansthe layer is no longer planar. Repeating the process over multiplelayers can result in even worse deviation from an ideal planar surface.Nonplanar surfaces pose problems for high-resolution photolithographywhich has a restricted depth of focus.

The present invention involves etch processes which have been found toform planar surfaces despite the presence of wide gaps and narrow gaps(a heterogeneous gap pattern) on damascene layer. The copper linesproduced using the methods disclosed herein display less resistance,reduced RC delay, and enable faster switching speeds in completeddevices. The methods of etching dielectric from between the copper linesinclude remote plasmas and specific classes of precursors and anoptional pretreatment using a local plasma. The plasmas effluents reactwith the dielectric to selectively remove the dielectric but only frombetween closely-spaced metal lines. The methods also do not require awet clean once the dielectric is removed and, therefore, removes therisk of pattern collapse.

In order to better understand and appreciate the invention, reference isnow made to FIG. 1 which is a flow chart of an air gap process 100according to embodiments. Simultaneously, reference will be made toFIGS. 2A-2H which are cross-sectional views of a patterned substrateduring the air gap process. A patterned low-K dielectric 210 is formed,patterned, and filled with copper lines 220. The structure is polishedor otherwise processed to expose portions of patterned low-k dielectric210 and copper lines 220. A hardmask layer is formed (operation 110) andpatterned (operation 120) on the underlying layer of patterned low-kdielectric 210 and copper lines 220. Photoresist 240 is used to form thepattern in hardmask layer 230 to form patterned hardmask layer 230-1.After the bulk of photoresist 240 is removed by ashing, residualphotoresist 240-1 is removed with a wet clean in operation 130.

The patterned substrate is then delivered into a substrate processingregion. Argon and helium are flowed into the substrate processing regionhousing the patterned substrate. The argon and helium are excited in alocal capacitively-coupled plasma within the substrate processing regionand exposed portions of patterned low-k dielectric 210 are treated inoperation 140. The treatment of exposed portions of patterned low-kdielectric 210 is hypothesized to remove methyl groups from thepatterned low-k dielectric 210, making the exposed portions behave morelike SiO than SiOC and making the exposed portions easier to remove withthe next operation. The treatment of exposed portions of patternedhardmask layer 230-1 is similarly hypothesized to remove methyl groupsfrom the patterned hardmask layer 230-1. The treatment makes thepatterned hardmask behave more like SiN than SiCN and eases removal ofpatterned hardmask 230-1, if it will be removed at all. Generallyspeaking, the substrate processing region may contain a pretreatment gaswhich includes or consist of one or more of argon, helium, nitrogen andhydrogen, in embodiments, during operation 140. The substrate processingregion may be devoid of oxygen during operation 140, in embodiments, tosuppress corrosion of copper and maintain a low dielectric constant inpatterned low-k dielectric 210.

Nitrogen trifluoride and hydrogen (H₂) are flowed into a plasma regionseparate from the substrate processing region housing the patternedsubstrate (operation 150). The separate plasma region may be referred toas a remote plasma region herein and may be a distinct module from theprocessing chamber or a compartment within the substrate processingchamber separated from the substrate processing region by a showerhead.Remote plasma effluents (i.e. products from the remote plasma) areflowed through the showerhead into the substrate processing region andallowed to interact with the patterned substrate surface, also inoperation 150, to remove exposed portions of patterned low-k dielectric210 to form recessed patterned low-k dielectric 210-1. Depending on thetemperature of the patterned substrate, solid by-product may or may notbe formed on recessed patterned low-k dielectric 210-1. If solidby-products are formed, they are removed by heating the patternedsubstrate above the sublimation temperature (not shown in air gapprocess 100). The reaction-sublimation process may be repeated untilpatterned low-k dielectric 210 is recessed to near the base of copperlines 220 as shown in FIG. 2D.

The estimated nature of the optional solid by-products is now described.Substrate temperatures which produce and do not produce solid residuewill be described shortly. When produced, the solid by-product mayconsume a top layer of patterned low-k dielectric 210 and the solidby-product possesses material from the plasma effluents and materialfrom patterned low-k dielectric 210. Plasma effluents produced fromnitrogen trifluoride and hydrogen (or ammonia) include a variety ofmolecules, molecular fragments and ionized species. Currentlyentertained theoretical mechanisms of the formation of the solidby-product may or may not be entirely correct but plasma effluents arethought to include HF which reacts readily with low temperaturepatterned low-k dielectric 210. Plasma effluents may react withpatterned low-k dielectric 210, in embodiments, to form (NH₄)₂SiF₆exhaustable gas products. The exhaustable gas products are vapors underthe processing conditions described herein and may be removed from thesubstrate processing region by a vacuum pump. A layer of (NH₄)₂SiF₆solid by-product is left behind on a dielectric portion of the patternedsubstrate surface. A variety of ratios of nitrogen trifluoride tohydrogen into the remote plasma region may be used, however, between 1:1and 4:1 or about a 2:1 ratio of hydrogen (or ammonia) to nitrogentrifluoride may be used according to embodiments.

Nitrogen trifluoride and hydrogen (H₂) are specific examples of afluorine-containing precursor and a hydrogen-containing precursor.Generally speaking, a fluorine-containing precursor may be flowed intothe remote plasma region and the fluorine-containing precursor mayinclude one or more of atomic fluorine, diatomic fluorine, brominetrifluoride, chlorine trifluoride, nitrogen trifluoride, hydrogenfluoride, sulfur hexafluoride and xenon difluoride. Evencarbon-containing precursors, such as carbon tetrafluoride,trifluoromethane, difluoromethane, fluoromethane and otherfluorocarbons, can be added to the group already listed. Similarly, ahydrogen-containing precursor flowed during operation 150 includes oneor more of atomic hydrogen, molecular hydrogen, ammonia, aperhydrocarbon and an incompletely halogen-substituted hydrocarbon. Theremote plasma region and/or the substrate processing region may bedevoid of oxygen in embodiments, however, other embodiments to bedescribed shortly do include oxygen.

Generally speaking, patterned low-k dielectric 210 may be a patterneddielectric layer with a variety of dielectric constants. Patterneddielectric in the layer may possess a dielectric constant below threeand a half, below three, below two and a half, or below two inembodiments. Hardmask layer 230 and patterned hardmask layer 230-1 weredescribed in the example as including silicon, carbon and nitrogen. Ingeneral, the hardmask layer may comprise or consist of silicon, carbon,nitrogen and hydrogen according to embodiments. The hardmask layer maycomprise or consist of silicon, carbon and nitrogen in embodiments. Thehard mask layer may be oxygen-free. A portion of the patterned hardmaskmaterial may be left on the patterned substrate during the etchprocesses described herein and may be left into the completed device.Alternatively, the hardmask material may be removed prior to depositingthe non-conformal dielectric layer, in embodiments, which will bedescribed shortly.

Between operation 140 and 150, the patterned substrate may betransferred between substrate processing chambers or may remain in thesame substrate processing chamber according to embodiments. Thetreatment of patterned low-k dielectric 210 and etching of patternedlow-k dielectric 210 may both occur in a combination remote/local plasmaetching chamber from Applied Materials, in which case no transfer isnecessary. As described later, the concentration of ions is suppressedin the substrate processing region of a some Applied Materialsprocessing chambers by incorporating an ion suppression element.Operation 150 may benefit from the use of the ion suppression element inembodiments. However, patterned low-k dielectric 210 may be recessedusing a remote plasma processing chamber which is not equipped with anion suppression element, in embodiments. Etching chambers are availablefrom Applied Materials which possess no ion suppression element butoffer integrated sublimation capabilities. The patterned substrate mayalso be transferred between separate substrate processing systemsprovided a continuous inert environment is provided for the substrate(i.e. no air-break is necessary during transfer). The exposed copperwould be corroded if exposed to an atmosphere containing oxygen.

Alternative chemistries have also been developed for operation 150.Flows of nitrogen trifluoride and dinitrogen oxide (N₂O) are introducedinto the remote plasma region. During this stage, little or no hydrogenis co-introduced into the remote plasma region according to embodiments.This fluorine-containing precursor may not be mixed with a source ofhydrogen, in embodiments, and the second plasma effluents may then beessentially devoid of hydrogen. A small amount of ammonia or hydrogen(e.g. less than 1:5 or 1:10 H:F atomic flow ratio) may be added withoutcorroding exposed portions of copper lines 220. Other sources offluorine may be used to augment or replace the nitrogen trifluoride. Ingeneral, a second fluorine-containing precursor may be flowed into theplasma region and the second fluorine-containing precursor comprises atleast one precursor selected from the group consisting of atomicfluorine, diatomic fluorine, bromine trifluoride, chlorine trifluoride,nitrogen trifluoride, hydrogen fluoride, sulfur hexafluoride, xenondifluoride, carbon tetrafluoride, trifluoromethane, difluoromethane,fluoromethane and fluorinated hydrocarbons. The plasma effluents formedin the remote plasma region are then flowed into the substrateprocessing region as before (operation 130) and patterned low-kdielectric 210 is selectively etched from the patterned substrate torecess the exposed portions as shown in FIG. 2F.

A conformal barrier layer 250 is optionally deposited in operation 160.A non-conformal dielectric layer 260 is then deposited on the copperlines 220 using a process with a very high sticking coefficient and lowmobility in operation 170. An exemplary process is a typicalplasma-enhanced chemical vapor deposition (PECVD) dielectric depositionprocess having high deposition rate. Depositing non-conformal dielectricin this way grow and join together to trap an air gap (gas pocket)between the two copper lines separated by the narrow gap. On the otherhand, the wide gap is still filled with patterned low-k dielectric. As aconsequence, non-conformal dielectric layer 260 is substantially planardespite forming air gaps in only a portion of the gaps between adjacentcopper lines 220.

The temperature of the patterned substrate during operation 140 may bebetween about 25° C. and about 175° C. according to embodiments. Thetemperature of the patterned substrate during operation 150 may be belowone of 60° C., 50° C., 40° C. or 35° C. in embodiments. The solidby-product formed during the first dry etch stage is removed prior tooperation 160 by sublimation. The temperature of the solid by-productand the patterned substrate may be raised above one of 90° C., 100° C.,120° C. or 140° C. during the sublimation according to embodiments.

The temperature during operation 150 may also be maintained at a higherlevel which promotes the simultaneous sublimation of solid residueby-product or does not form solid residue by-product in the first place.Therefore, the temperature of the patterned substrate during operation150 may be less than about one of 160° C., less than 140° C., less than120° C. or less than 100° C. during the sublimation according toembodiments. Additional patterned substrate temperatures will beprovided in the course of describing exemplary equipment. Somechemistries described herein do not form solid by-products regardless oftemperature.

During operation 150, a nitrogen-and-oxygen-containing precursor may beused in place of the exemplary nitrous oxide (N₂O). More generally, anitrogen-and-oxygen-containing precursor is flowed into the remoteplasma system and the nitrogen-and-oxygen-containing precursor maycomprise at least one precursor selected from N₂O, NO, N₂O₂, NO₂. Thenitrogen-and-oxygen-containing precursor may also be a combination of asource of nitrogen (e.g. N₂) and a source of oxygen (O₂) according toembodiments. The nitrogen-and-oxygen-containing precursor may consistessentially of or consist of nitrogen and oxygen. Somenitrogen-and-oxygen-containing precursors may be very electronegativeand benefit a high plasma power to form oxidizing plasma effluents. Thenitrous oxide may be excited in a supplementary plasma before flowingthe oxidizing plasma effluents so-generated into another remote plasmaused to also excite the fluorine-containing precursor. The supplementaryremote plasma is upstream from the remote plasma region in thateffluents generally flow from the supplementary remote plasma into theremote plasma region, but not vice versa. Thenitrogen-and-oxygen-containing precursor and the fluorine-containingprecursor may be excited in separate remote plasmas and first combine inthe substrate processing region according to embodiments.

During operation 150, the fluorine-containing precursor and/or thehydrogen-containing precursor may further include one or more relativelyinert gases such as He, N₂, Ar, or another inert gas. Argon may be addedto the plasma to make a plasma easier to form. Helium may be added toimprove uniformity of the plasma and the subsequent process. In anembodiment, the fluorine-containing precursor is provided at a flow rateof between about 5 sccm (standard cubic centimeters per minute) and 300sccm, hydrogen at a flow rate of between about 10 sccm and 600 sccm(standard liters per minute), He at a flow rate of between about 0 sccmand 5 slm, and Ar at a flow rate of between about 0 sccm and 5 slm.During operation 150, the fluorine-containing precursor and/or thenitrogen-and-oxygen-containing precursor may further include one or morerelatively inert gases such as He, N₂, Ar, or another inert gas. Argonmay be added to the plasma to make a plasma easier to form. Helium maybe added to improve uniformity of the plasma and the subsequent process.In an embodiment, the fluorine-containing precursor is provided at aflow rate of between about 5 sccm (standard cubic centimeters perminute) and 300 sccm, the nitrogen-and-oxygen-containing precursor at aflow rate of between about 250 sccm and 5 slm (standard liters perminute), He at a flow rate of between about 0 sccm and 5 slm, and Ar ata flow rate of between about 0 sccm and 5 slm. Little or essentially noNH₃ (or other hydrogen-containing precursor) is flowed during operation150, in embodiments, when a nitrogen-and-oxygen-containing precursor isused. The second remote plasma region and the second substrateprocessing region may be devoid of hydrogen during operation 150 inembodiments. Additional flow rate embodiments are provided in the courseof describing exemplary equipment. One of ordinary skill in the artwould recognize that other gases and/or flows may be used depending on anumber of factors including processing chamber configuration, substratesize, geometry and layout of features being etched.

The flow of N₂O (or another nitrogen-and-oxygen-containing precursor)into the remote plasma system and then into the remote plasma regionresults in a flow of oxidizing plasma effluents (which containradical-nitrogen-oxygen) into the substrate processing region. Plasmaeffluents will be used herein to encompass the fluorine-containingplasma effluents and the oxidizing plasma effluents. The oxidizingplasma effluents include radical-nitrogen-oxygen. Theradical-nitrogen-oxygen is thought to contain nitric oxide (NO), whichis too reactive to directly deliver to the substrate processing region.The radical-nitrogen-oxygen contains radicals which comprise nitrogenand oxide and may consist of nitrogen and oxide in embodiments. Theradical-nitrogen-oxygen is a component of the plasma effluents whichflow into the substrate processing region in embodiments of operation150. The plasma effluents also comprise radical-fluorine formed from theflow of the fluorine-containing precursor into the remote plasma region.The flow of radical-nitrogen-oxygen into the substrate processing regionenables the radical-fluorine to remove the patterned low-k dielectric210 while limiting the reaction rate with exposed copper lines 220. Theflow of radical-nitrogen-oxygen into the substrate processing region haslittle effect on the exposed regions of copper and the radical-fluorineis substantially unable to etch the copper.

During operation 140, the method includes applying energy to thepretreatment gas in the substrate processing region. The plasma may begenerated using known techniques (e.g., RF, capacitively coupled,inductively coupled). In an embodiment, the energy is applied to theremote plasma region using a capacitively-coupled plasma unit at asource power of between about 5 watts and about 2000 watts or betweenabout 10 watts and about 1000 watts, in embodiments. The pressure in thesubstrate processing region may be between about 2 mTorr and about 1Torr or between about 5 mTorr and about 500 mTorr, according toembodiments. The RF frequency applied to excite the local plasma ofpretreatment gas may be between about 30 kHz and about 3 GHz. Forexample, the RF frequency may be low RF frequencies less than about 200kHz, high RF frequencies between about 10 MHz and about 15 MHz ormicrowave frequencies greater than or about 1 GHz according toembodiments.

During operation 150, the method includes applying energy to thefluorine-containing precursor (and the hydrogen-containing ornitrogen-and-oxygen-containing precursors in different embodiments) inthe remote plasma region to generate the plasma effluents. As would beappreciated by one of ordinary skill in the art, the plasma may includea number of charged and neutral species including radicals and ions. Theplasma may be generated using known techniques (e.g., RF, capacitivelycoupled, inductively coupled). In an embodiment, the energy is appliedto the remote plasma region using a capacitively-coupled plasma unit ata source power of between about 20 watts and about 3000 watts or betweenabout 50 watts and about 2000 watts, in embodiments. The pressure in theremote plasma region (and the substrate processing region) may bebetween about 0.25 Torr and about 30 Torr or between about 0.5 Torr andabout 20 Torr, according to embodiments. The RF frequency applied toexcite the remote plasma of fluorine-containing precursor and anysupplementary precursors may be between about 1 MHz and about 100 MHz orbetween about 2 MHz and about 60 MHz in embodiments.

In operation 170, the non-conformal layer of dielectric may comprisesilicon oxide or a preferably a low-k dielectric (e.g. SiOC or SiOCH) inembodiments. Material in the non-conformal layer of dielectric maypossess a dielectric constant below three and a half, below three, belowtwo and a half, or below two according to embodiments. The hardmasklayer has more latitude, especially since it may be a leave-on film. Thehardmask layer may be one of silicon carbon nitride, silicon nitride,aluminum oxide, tantalum oxide or titanium oxide in embodiments.

The exemplary copper lines of FIGS. 2A-2H may have a conformal barrierlayer (e.g. a titanium lining layer) included, in part, to discouragediffusion of copper into the sensitive electronic components. Ingeneral, the conformal barrier layer may be a variety of materialsincluding silicon carbon nitride and silicon nitride. The air gap formedin air gap processes described herein may extend all the way to thelining layer bordering each of two adjacent conducting lines inembodiments. The air gap, at its widest point, may extend at least 80%of the way between two adjacent conducting lines on either side of thenarrow gap according to embodiments. The narrow gap may be less than orabout 20 nm wide, less than or about 15 nm wide, or less than or about12 nm wide in embodiments. The wide gap may be greater than or abouttwice the width of the narrow gap, two and a half times the width of thenarrow gap, or three times the width of the narrow gap according toembodiments.

In general, conducting lines may comprise several conducting material incombination. Conducting lines are separate from the dielectric conformalbarrier layer described above (e.g. conformal barrier layer 250).Conducting lines may comprise copper, cobalt or tungsten according toembodiments. Copper may benefit from a conducting barrier layer such astantalum, tantalum nitride, titanium nitride or titanium in embodiments.Certain applications may include conducting barrier layers in otherconducting lines besides copper. When a conducting barrier layer isincluded, the extent of the conducting line includes the conductingbarrier layer as well. For example, copper lines 220 in FIGS. 2A-2H arehomogeneous in the figures but may include a conducting barrier layerwithin the homogeneous region shown. An air gap may extend at least 80%across the narrow gap, in embodiments, and 100% of the narrow gap ismeasured from the outer edge of one conducting barrier to another, whena conducting barrier is included. If no conducting barrier is included,100% of the narrow gap is measured from the outer edge of the bulk metal(e.g. copper, cobalt or tungsten). Conducting lines may comprise orconsist of copper, cobalt or tungsten in embodiments. Conducting linesmay alternatively comprise or consist of one or more of copper,titanium, tantalum or nitrogen according to embodiments.

In embodiments, local plasma treatment may occur before etching low-kmaterial from the narrow gaps. Similarly, etching low-k material fromthe narrow gaps may occur before forming non-conformal low-k dielectricon the two adjacent copper lines separated by the narrow gap to form theair gap.

In embodiments, an ion suppressor as described in the exemplaryequipment section may be used to provide radical and/or neutral speciesfor selectively etching silicon nitride. The ion suppressor may also bereferred to as an ion suppression element. In embodiments, for example,the ion suppressor is used to filter etching plasma effluents (includingradical-fluorine) to selectively etch silicon nitride. The ionsuppressor may be included in each exemplary process described herein.

The ion suppressor may be used to provide a reactive gas having a higherconcentration of radicals than ions. The ion suppressor functions todramatically reduce or substantially eliminate ionically charged speciestraveling from the plasma generation region to the substrate. Theelectron temperature may be measured using a Langmuir probe in thesubstrate processing region during excitation of a plasma in the remoteplasma region on the other side of the ion suppressor. In embodiments,the electron temperature may be less than 0.5 eV, less than 0.45 eV,less than 0.4 eV, or less than 0.35 eV. These extremely low values forthe electron temperature are enabled by the presence of the showerheadand/or the ion suppressor positioned between the substrate processingregion and the remote plasma region. Uncharged neutral and radicalspecies may pass through the openings in the ion suppressor to react atthe substrate. Because most of the charged particles of a plasma arefiltered or removed by the ion suppressor, the substrate is notnecessarily biased during operation 130. Such a process using radicalsand other neutral species can reduce plasma damage compared toconventional plasma etch processes that include sputtering andbombardment. The ion suppressor helps control the concentration of ionicspecies in the reaction region at a level that assists the process.Embodiments of the present invention are also advantageous overconventional wet etch processes where surface tension of liquids cancause bending and peeling of small features.

Additional process parameters are disclosed in the course of describingan exemplary processing chamber and system.

Exemplary Processing Equipment

FIG. 3A is a substrate processing chamber 1001 according to embodiments.A remote plasma system 1010 may process the fluorine-containingprecursor which then travels through a gas inlet assembly 1011. Twodistinct gas supply channels are visible within the gas inlet assembly1011. A first channel 1012 conducts a precursor that has just passedthrough the remote plasma system 1010 (RPS), while a second channel 1013conducts a precursor that has bypassed the remote plasma system 1010.The first channel 1012 conducts the nitrogen-and-oxygen-containingprecursor and the second channel 1013 conducts the fluorine-containingprecursor.

The lid (or conductive top portion) 1021 and a perforated partition 1053are shown with an insulating ring 1024 in between, which allows an ACpotential to be applied to the lid 1021 relative to perforated partition1053. The AC potential strikes a plasma in chamber plasma region 1020.The fluorine-containing precursor may flow through second channel 1013and is excited by chamber plasma region 1020 and not RPS 1010. Theperforated partition (also referred to as a showerhead) 1053 separateschamber plasma region 1020 from a substrate processing region 1070beneath showerhead 1053. Showerhead 1053 allows a plasma present inchamber plasma region 1020 to avoid directly exciting gases in substrateprocessing region 1070, while still allowing excited species to travelfrom chamber plasma region 1020 into substrate processing region 1070.

Showerhead 1053 is positioned between chamber plasma region 1020 andsubstrate processing region 1070 and allows plasma effluents (excitedderivatives of precursors or other gases) created within remote plasmasystem 1010 and/or chamber plasma region 1020 to pass through aplurality of through-holes 1056 that traverse the thickness of theplate. The showerhead 1053 also has one or more hollow volumes 1051which can be filled, in embodiments, with a precursor in the form of avapor or gas (such as an oxidizing plasma effluents excited in RPS 1010)and pass through small holes 1055 into substrate processing region 1070but not directly into chamber plasma region 1020. Small holes 1055 maybe described as blind holes to convey that they are not fluidly coupleddirectly to chamber plasma region 1020 like through-holes 1056.Showerhead 1053 is thicker than the length of the smallest diameter 1050of the through-holes 1056 in this disclosed embodiment. To maintain asignificant concentration of excited species penetrating from chamberplasma region 1020 to substrate processing region 1070, the length 1026of the smallest diameter 1050 of the through-holes may be restricted byforming larger diameter portions of through-holes 1056 part way throughthe showerhead 1053. The length of the smallest diameter 1050 of thethrough-holes 1056 may be the same order of magnitude as the smallestdiameter of the through-holes 1056 or less in embodiments.

Showerhead 1053 may be configured to serve the purpose of an ionsuppressor as shown in FIG. 3A. Alternatively, a separate processingchamber element may be included (not shown) which suppresses the ionconcentration traveling into substrate processing region 1070. Lid 1021and showerhead 1053 may function as a first electrode and secondelectrode, respectively, so that lid 1021 and showerhead 1053 mayreceive different electric voltages. In these configurations, electricalpower (e.g., RF power) may be applied to lid 1021, showerhead 1053, orboth. For example, electrical power may be applied to lid 1021 whileshowerhead 1053 (serving as ion suppressor) is grounded. The substrateprocessing system may include a RF generator that provides electricalpower to the lid and/or showerhead 1053. The voltage applied to lid 1021may facilitate a uniform distribution of plasma (i.e., reduce localizedplasma) within chamber plasma region 1020. To enable the formation of aplasma in chamber plasma region 1020, insulating ring 1024 mayelectrically insulate lid 1021 from showerhead 1053. Insulating ring1024 may be made from a ceramic and may have a high breakdown voltage toavoid sparking. Portions of substrate processing chamber 1001 near thecapacitively-coupled plasma components just described may furtherinclude a cooling unit (not shown) that includes one or more coolingfluid channels to cool surfaces exposed to the plasma with a circulatingcoolant (e.g., water).

In the embodiment shown, showerhead 1053 may distribute (viathrough-holes 1056) process gases which contain oxygen, fluorine and/ornitrogen and/or plasma effluents of such process gases upon excitationby a plasma in chamber plasma region 1020. According to embodiments, theprocess gas introduced into the remote plasma system 1010 and/or chamberplasma region 1020 may contain fluorine (e.g. F₂, NF₃ or XeF₂). Theprocess gas may also include a carrier gas such as helium, argon,nitrogen (N₂), etc. Plasma effluents may include ionized or neutralderivatives of the process gas and may also be referred to herein asradical-fluorine referring to the atomic constituent of the process gasintroduced.

Through-holes 1056 are configured to suppress the migration ofionically-charged species out of the chamber plasma region 1020 whileallowing uncharged neutral or radical species to pass through showerhead1053 into substrate processing region 1070. These uncharged species mayinclude highly reactive species that are transported with less-reactivecarrier gas by through-holes 1056. As noted above, the migration ofionic species by through-holes 1056 may be reduced, and in someinstances completely suppressed or essentially eliminated. Controllingthe amount of ionic species passing through showerhead 1053 providesincreased control over the gas mixture brought into contact with theunderlying wafer substrate, which in turn increases control of thedeposition and/or etch characteristics of the gas mixture. For example,adjustments in the ion concentration of the gas mixture cansignificantly alter its etch selectivity.

According to embodiments, the number of through-holes 1056 may bebetween about 60 and about 2000. Through-holes 1056 may have a varietyof shapes but are most easily made round. The smallest diameter 1050 ofthrough-holes 1056 may be between about 0.5 mm and about 20 mm orbetween about 1 mm and about 6 mm in embodiments. There is alsoflexibility in choosing the cross-sectional shape of through-holes,which may be made conical, cylindrical or combinations of the twoshapes. The number of small holes 1055 used to introduce unexcitedprecursors into substrate processing region 1070 may be between about100 and about 5000 or between about 500 and about 2000 in embodiments.The diameter of the small holes 1055 may be between about 0.1 mm andabout 2 mm.

Through-holes 1056 may be configured to control the passage of theplasma-activated gas (i.e., the ionic, radical, and/or neutral species)through showerhead 1053. For example, the aspect ratio of the holes(i.e., the hole diameter to length) and/or the geometry of the holes maybe controlled so that the flow of ionically-charged species in theactivated gas passing through showerhead 1053 is reduced. Through-holes1056 in showerhead 1053 may include a tapered portion that faces chamberplasma region 1020, and a cylindrical portion that faces substrateprocessing region 1070. The cylindrical portion may be proportioned anddimensioned to control the flow of ionic species passing into substrateprocessing region 1070. An adjustable electrical bias may also beapplied to showerhead 1053 as an additional means to control the flow ofionic species through showerhead 1053.

Alternatively, through-holes 1056 may have a smaller inner diameter (ID)toward the top surface of showerhead 1053 and a larger ID toward thebottom surface. Through holes 1056 may have a larger inner diametertoward the top surface of showerhead 1053 and a smaller inner diametertoward the bottom surface of the showerhead. In addition, the bottomedge of through-holes 1056 may be chamfered to help evenly distributethe plasma effluents in substrate processing region 1070 as the plasmaeffluents exit the showerhead and promotes even distribution of theplasma effluents and precursor gases. The smaller ID may be placed at avariety of locations along through-holes 1056 and still allow showerhead1053 to reduce the ion density within substrate processing region 1070.The reduction in ion density results from an increase in the number ofcollisions with walls prior to entry into substrate processing region1070. Each collision increases the probability that an ion isneutralized by the acquisition or loss of an electron from the wall.Generally speaking, the smaller ID of through-holes 1056 may be betweenabout 0.2 mm and about 20 mm. According to embodiments, the smaller IDmay be between about 1 mm and 6 mm or between about 0.2 mm and about 5mm. Further, aspect ratios of the through-holes 1056 (i.e., the smallerID to hole length) may be approximately 1 to 20. The smaller ID of thethrough-holes may be the minimum ID found along the length of thethrough-holes. The cross sectional shape of through-holes 1056 may begenerally cylindrical, conical, or any combination thereof.

FIG. 3B is a bottom view of a showerhead 1053 for use with a processingchamber according to embodiments. Showerhead 1053 corresponds with theshowerhead shown in FIG. 3A. Through-holes 1056 are depicted with alarger inner-diameter (ID) on the bottom of showerhead 1053 and asmaller ID at the top. Small holes 1055 are distributed substantiallyevenly over the surface of the showerhead, even amongst thethrough-holes 1056 which helps to provide more even mixing inembodiments.

An exemplary patterned substrate may be supported by a pedestal (notshown) within substrate processing region 1070 when fluorine-containingplasma effluents arrive through through-holes 1056 in showerhead 1053.Though substrate processing region 1070 may be equipped to support aplasma for other processes such as curing, no plasma is present duringthe etching of patterned substrate, in embodiments.

A plasma may be ignited either in chamber plasma region 1020 aboveshowerhead 1053 or substrate processing region 1070 below showerhead1053. A plasma is present in chamber plasma region 1020 to produce theradical-fluorine from an inflow of the fluorine-containing precursor. AnAC voltage typically in the radio frequency (RF) range is appliedbetween the conductive top portion (lid 1021) of the processing chamberand showerhead 1053 to ignite a plasma in chamber plasma region 1020during deposition. An RF power supply generates a high RF frequency of13.56 MHz but may also generate other frequencies alone or incombination with the 13.56 MHz frequency.

The top plasma may be left at low or no power when the bottom plasma inthe substrate processing region 1070 is turned on to either cure a filmor clean the interior surfaces bordering substrate processing region1070. A plasma in substrate processing region 1070 is ignited byapplying an AC voltage between showerhead 1053 and the pedestal orbottom of the chamber. A cleaning gas may be introduced into substrateprocessing region 1070 while the plasma is present.

The pedestal may have a heat exchange channel through which a heatexchange fluid flows to control the temperature of the substrate. Thisconfiguration allows the substrate temperature to be cooled or heated tomaintain relatively low temperatures (from −20° C. through about 120°C.). The heat exchange fluid may comprise ethylene glycol and water. Thewafer support platter of the pedestal (preferably aluminum, ceramic, ora combination thereof) may also be resistively heated to achieverelatively high temperatures (from about 120° C. through about 1100° C.)using an embedded single-loop embedded heater element configured to maketwo full turns in the form of parallel concentric circles. An outerportion of the heater element may run adjacent to a perimeter of thesupport platter, while an inner portion runs on the path of a concentriccircle having a smaller radius. The wiring to the heater element passesthrough the stem of the pedestal.

The chamber plasma region or a region in a remote plasma system may bereferred to as a remote plasma region. In embodiments, the radicalprecursors (e.g. radical-fluorine and radical-nitrogen-oxygen) areformed in the remote plasma region and travel into the substrateprocessing region where the combination preferentially etches siliconnitride. Plasma power may essentially be applied only to the remoteplasma region, in embodiments, to ensure that the radical-fluorine andany supplementary radical sources (which together may be referred to asplasma effluents) are not further excited in the substrate processingregion.

In embodiments employing a chamber plasma region, the excited plasmaeffluents are generated in a section of the substrate processing regionpartitioned from a deposition region. The deposition region, also knownherein as the substrate processing region, is where the plasma effluentsmix and react to etch the patterned substrate (e.g., a semiconductorwafer). The excited plasma effluents may also be accompanied by inertgases (in the exemplary case, helium). The substrate processing regionmay be described herein as “plasma-free” during the etch processes(operation 120 and 130) of the patterned substrate. “Plasma-free” doesnot necessarily mean the region is devoid of plasma. A relatively lowconcentration of ionized species and free electrons created within theplasma region do travel through pores (apertures) in the partition(showerhead/ion suppressor) due to the shapes and sizes of through-holes1056. In some embodiments, there is essentially no concentration ofionized species and free electrons within the substrate processingregion. The borders of the plasma in the chamber plasma region are hardto define and may encroach upon the substrate processing region throughthe apertures in the showerhead. In the case of an inductively-coupledplasma, a small amount of ionization may be effected within thesubstrate processing region directly. Furthermore, a low intensityplasma may be created in the substrate processing region withouteliminating features of the forming film. All causes for a plasma havingmuch lower intensity ion density than the chamber plasma region (or aremote plasma region, for that matter) during the creation of theexcited plasma effluents do not deviate from the scope of “plasma-free”as used herein.

Nitrogen trifluoride (or another fluorine-containing precursor) may beflowed into chamber plasma region 1020 at rates between about 5 sccm andabout 500 sccm, between about 10 sccm and about 300 sccm, between about25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm orbetween about 75 sccm and about 125 sccm in embodiments. Optionally,ammonia (or another hydrogen-containing precursor) may be flowed intochamber plasma region 1020 at rates between about 10 sccm and about 1000sccm, between about 20 sccm and about 600 sccm, between about 50 sccmand about 400 sccm, between about 100 sccm and about 300 sccm or betweenabout 150 sccm and about 250 sccm in embodiments. Supplementaryprecursors may be flowed into remote plasma region 1010 and then chamberplasma region 1020 (in series) at rates greater than or about 250 sccm,greater than or about 500 sccm, greater than or about 1 slm, greaterthan or about 2 slm or greater than or about 5 slm in embodiments.

A flow rate of fluorine-containing precursor into the chamber mayaccount for 0.05% to about 20% by volume of the overall gas mixture; theremainder being carrier gases. The fluorine-containing precursor isflowed into the remote plasma region but the plasma effluents have thesame volumetric flow ratio, according to embodiments. In the case of thefluorine-containing precursor, a purge or carrier gas may be firstinitiated into the remote plasma region before those of thefluorine-containing gas to stabilize the pressure within the remoteplasma region.

Plasma power applied to the first remote plasma region and the secondremote plasma region can be a variety of frequencies or a combination ofmultiple frequencies and may be different between the two remoteplasmas. In the exemplary processing system the second remote plasma isprovided by RF power delivered between lid 1021 and showerhead 1053. TheRF power applied to the first remote plasma region (RPS 1010 in theexample) may be between about 250 watts and about 15000 watts, betweenabout 500 watts and about 5000 watts, or between about 1000 watts andabout 2000 watts in embodiments. The RF power applied to the secondremote plasma region (chamber plasma region 1020 in the example) may bebetween about 10 watts and about 1500 watts, between about 20 watts andabout 1000 watts, between about 50 watts and about 500 watts, or betweenabout 100 watts and about 200 watts according to embodiments. The RFfrequency applied in the exemplary processing system may be low RFfrequencies less than about 200 kHz, high RF frequencies between about10 MHz and about 15 MHz or microwave frequencies greater than or about 1GHz according to embodiments.

The temperature of the substrate may be between about −30° C. and about150° C. during operations 120 and/or 130. The etch rate has been foundto be higher for the lower temperatures within this range. Inembodiments, the temperature of the substrate during the etch processesdescribed herein is about −20° C. or more, 0° C. or more, about 5° C. ormore or about 10° C. or more. The substrate temperatures may be lessthan or about 150° C., less than or about 100° C., less than or about50° C., less than or about 30° C., less than or about 20° C., less thanor about 15° C. or less than or about 10° C. in embodiments. Any of theupper limits on temperature or pressure may be combined with lowerlimits to form additional embodiments.

Substrate processing region 1070, remote plasma system 1010 or chamberplasma region 1020 can be maintained at a variety of pressures duringthe flow of carrier gases and plasma effluents into substrate processingregion 1070. The pressure within the substrate processing region isbelow or about 50 Torr, below or about 30 Torr, below or about 20 Torr,below or about 10 Torr or below or about 5 Torr. The pressure may beabove or about 0.01 Torr, above or about 0.1 Torr, above or about 0.2Torr, above or about 0.5 Torr or above or about 1 Torr in embodiments.Lower limits on the pressure may be combined with upper limits on thepressure to form additional embodiments. The data show an increase inetch rate as a function of process pressure and an associated increasein loading effect, which may or may not be desirable or tolerated for agiven process flow.

In embodiments, the substrate processing chamber 1001 can be integratedinto a variety of multi-processing platforms, including the Producer™GT, Centura™ AP and Endura™ platforms available from Applied Materials,Inc. located in Santa Clara, Calif. Such a processing platform iscapable of performing several processing operations without breakingvacuum. Processing chambers that may implement methods disclosed hereinmay include dielectric etch chambers or a variety of chemical vapordeposition chambers, among other types of chambers.

Processing chambers may be incorporated into larger fabrication systemsfor producing integrated circuit chips. FIG. 4 shows one such system1101 of deposition, baking and curing chambers according to embodiments.In the figure, a pair of FOUPs (front opening unified pods) 1102 supplysubstrate substrates (e.g., 300 mm diameter wafers) that are received byrobotic arms 1104 and placed into a low pressure holding areas 1106before being placed into one of the wafer processing chambers 1108 a-f.A second robotic arm 1110 may be used to transport the substrate wafersfrom the low pressure holding areas 1106 to the wafer processingchambers 1108 a-f and back. Each wafer processing chamber 1108 a-f, canbe outfitted to perform a number of substrate processing operationsincluding the dry etch processes described herein in addition tocyclical layer deposition (CLD), atomic layer deposition (ALD), chemicalvapor deposition (CVD), physical vapor deposition (PVD), etch,pre-clean, degas, orientation and other substrate processes.

The wafer processing chambers 1108 a-f may include one or more systemcomponents for depositing, annealing, curing and/or etching a dielectricfilm on the substrate wafer. In one configuration, two pairs of theprocessing chamber (e.g., 1108 c-d and 1108 e-f) may be used to depositdielectric material on the substrate, and the third pair of processingchambers (e.g., 1108 a-b) may be used to etch the deposited dielectric.In another configuration, all three pairs of chambers (e.g., 1108 a-f)may be configured to etch a dielectric film on the substrate. Any one ormore of the processes described may be carried out on chamber(s)separated from the fabrication system shown in embodiments.

The substrate processing system is controlled by a system controller. Inan exemplary embodiment, the system controller includes a hard diskdrive, a floppy disk drive and a processor. The processor contains asingle-board computer (SBC), analog and digital input/output boards,interface boards and stepper motor controller boards. Various parts ofCVD system conform to the Versa Modular European (VME) standard whichdefines board, card cage, and connector dimensions and types. The VMEstandard also defines the bus structure as having a 16-bit data bus anda 24-bit address bus.

System controller 1157 is used to control motors, valves, flowcontrollers, power supplies and other functions required to carry outprocess recipes described herein. A gas handling system 1155 may also becontrolled by system controller 1157 to introduce gases to one or all ofthe wafer processing chambers 1108 a-f. System controller 1157 may relyon feedback from optical sensors to determine and adjust the position ofmovable mechanical assemblies in gas handling system 1155 and/or inwafer processing chambers 1108 a-f. Mechanical assemblies may includethe robot, throttle valves and susceptors which are moved by motorsunder the control of system controller 1157.

In an exemplary embodiment, system controller 1157 includes a hard diskdrive (memory), USB ports, a floppy disk drive and a processor. Systemcontroller 1157 includes analog and digital input/output boards,interface boards and stepper motor controller boards. Various parts ofmulti-chamber processing system 1101 which contains substrate processingchamber 1001 are controlled by system controller 1157. The systemcontroller executes system control software in the form of a computerprogram stored on computer-readable medium such as a hard disk, a floppydisk or a flash memory thumb drive. Other types of memory can also beused. The computer program includes sets of instructions that dictatethe timing, mixture of gases, chamber pressure, chamber temperature, RFpower levels, susceptor position, and other parameters of a particularprocess.

A process for etching, depositing or otherwise processing a film on asubstrate or a process for cleaning chamber can be implemented using acomputer program product that is executed by the controller. Thecomputer program code can be written in any conventional computerreadable programming language: for example, 68000 assembly language, C,C++, Pascal, Fortran or others. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor, andstored or embodied in a computer usable medium, such as a memory systemof the computer. If the entered code text is in a high level language,the code is compiled, and the resultant compiler code is then linkedwith an object code of precompiled Microsoft Windows® library routines.To execute the linked, compiled object code the system user invokes theobject code, causing the computer system to load the code in memory. TheCPU then reads and executes the code to perform the tasks identified inthe program.

The interface between a user and the controller may be via atouch-sensitive monitor and may also include a mouse and keyboard. Inone embodiment two monitors are used, one mounted in the clean room wallfor the operators and the other behind the wall for the servicetechnicians. The two monitors may simultaneously display the sameinformation, in which case only one is configured to accept input at atime. To select a particular screen or function, the operator touches adesignated area on the display screen with a finger or the mouse. Thetouched area changes its highlighted color, or a new menu or screen isdisplayed, confirming the operator's selection.

As used herein “substrate” may be a support substrate with or withoutlayers formed thereon. The patterned substrate may be an insulator or asemiconductor of a variety of doping concentrations and profiles andmay, for example, be a semiconductor substrate of the type used in themanufacture of integrated circuits. Exposed “silicon” of the patternedsubstrate is predominantly Si but may include minority concentrations ofother elemental constituents such as nitrogen, oxygen, hydrogen andcarbon. Exposed “silicon oxycarbide” (a low-k dielectric) of thepatterned substrate is predominantly silicon, oxygen, carbon andhydrogen, but may include minority concentrations of other elementalconstituents. Exposed “silicon oxide” of the patterned substrate ispredominantly SiO₂ but may include minority concentrations of otherelemental constituents such as nitrogen, hydrogen and carbon. In someembodiments, silicon oxide films discussed herein consist essentially ofsilicon and oxygen.

The term “precursor” is used to refer to any process gas which takespart in a reaction to either remove material from or deposit materialonto a surface. “Plasma effluents” describe gas exiting from the chamberplasma region and entering the substrate processing region. Plasmaeffluents are in an “excited state” wherein at least some of the gasmolecules are in vibrationally-excited, dissociated and/or ionizedstates. A “radical precursor” is used to describe plasma effluents (agas in an excited state which is exiting a plasma) which participate ina reaction to either remove material from or deposit material on asurface. “Radical-fluorine” (or e.g. “radical-hydrogen”) are radicalprecursors which contain fluorine (or hydrogen) but may contain otherelemental constituents. The phrase “inert gas” refers to any gas whichdoes not form chemical bonds in the film during or after the etchprocess. Exemplary inert gases include noble gases but may include othergases so long as no chemical bonds are formed when (typically) traceamounts are trapped in a film.

The terms “gap” and “trench” are used throughout with no implicationthat the etched geometry has a large horizontal aspect ratio. Viewedfrom above the surface, trenches may appear circular, oval, polygonal,rectangular, or a variety of other shapes. A trench may be in the shapeof a moat around an island of material. The term “via” is used to referto a low aspect ratio trench (as viewed from above) which may or may notbe filled with metal to form a vertical electrical connection. As usedherein, a conformal etch process refers to a generally uniform removalof material on a surface in the same shape as the surface, i.e., thesurface of the etched layer and the pre-etch surface are generallyparallel. A person having ordinary skill in the art will recognize thatthe etched interface likely cannot be 100% conformal and thus the term“generally” allows for acceptable tolerances.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of thedisclosed embodiments. Additionally, a number of well known processesand elements have not been described to avoid unnecessarily obscuringthe present invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the dielectric material”includes reference to one or more dielectric materials and equivalentsthereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

1. A method of forming air gaps between conducting lines, the methodcomprising: forming and patterning a hardmask layer on a patternedsubstrate, wherein the patterned hard mask layer does not coverdielectric material in a narrow gap between two adjacent conductinglines but does cover dielectric material in a wide gap between two otheradjacent conducting lines; flowing a pretreatment gas into a substrateprocessing region housing the patterned substrate while forming a localplasma in the substrate processing region to treat the dielectric in thenarrow gap; flowing a fluorine-containing precursor into a remote plasmaregion separated from the substrate processing region by a showerheadwhile forming a remote plasma in the remote plasma region to form plasmaeffluents; flowing the plasma effluents into the substrate processingregion to etch the dielectric material from the narrow gap whileretaining the dielectric material in the wide gap; and forming anon-conformal layer of dielectric on the patterned substrate, whereindielectric formed on each conducting line grow and join together to trapan air gap in the narrow gap while the wide gap remains filled withdielectric material.
 2. The method of claim 1 wherein thefluorine-containing precursor comprises a precursor selected from thegroup consisting of nitrogen trifluoride, hydrogen fluoride, atomicfluorine, diatomic fluorine, a fluorocarbon and xenon difluoride.
 3. Themethod of claim 1 wherein the operation of flowing thefluorine-containing precursor into the remote plasma region furthercomprises flowing a hydrogen-containing precursor into the remote plasmaregion.
 4. The method of claim 3 wherein the hydrogen-containingprecursor comprises one of atomic hydrogen, molecular hydrogen, ammonia,a perhydrocarbon and an incompletely halogen-substituted hydrocarbon. 5.The method of claim 1 wherein the dielectric material is a low-kdielectric having dielectric constant less than three.
 6. The method ofclaim 1 wherein the operation of flowing the fluorine-containingprecursor into the remote plasma region further comprises flowing anitrogen-and-oxygen-containing precursor into the remote plasma region.7. The method of claim 6 wherein the nitrogen-and-oxygen-containingprecursor comprises one or more of N₂/O₂, N₂O, NO, NO₂ or N₂O₂.
 8. Themethod of claim 6 wherein the nitrogen-and-oxygen-containing precursorconsists of nitrogen and oxygen.
 9. The method of claim 1 wherein thehardmask layer is oxygen-free.
 10. The method of claim 1 wherein thehardmask layer comprises silicon, carbon and nitrogen.
 11. The method ofclaim 1 wherein the local plasma is a capacitively-coupled plasma andthe remote plasma is a capacitively-coupled plasma.
 12. The method ofclaim 1 wherein the narrow gap is less than or about 15 nm wide.
 13. Themethod of claim 1 wherein the wide gap is more than twice as wide as thenarrow gap.
 14. The method of claim 1 wherein the air gap, at its widestpoint, extends at least 80% of the way between two adjacent conductinglines on either side of the narrow gap.
 15. A method of forming air gapsbetween copper lines on a patterned substrate, the method comprising:patterning a low-k dielectric layer on the patterned substrate;depositing copper on the patterned low-k dielectric layer; planarizingthe copper to expose a narrow gap between two adjacent copper lines anda wide gap between two other adjacent copper lines; forming andpatterning a hardmask layer, wherein the patterned hard mask layercovers low-k material in the wide gap but does not cover low-k materialin the narrow gap; flowing a pretreatment gas into a substrateprocessing region housing the patterned substrate while forming a localplasma in the substrate processing region to treat the low-k material inthe narrow gap; flowing NF₃ into a remote plasma region separated fromthe substrate processing region by a showerhead while forming a remoteplasma in the remote plasma region to form plasma effluents; flowing theplasma effluents into the substrate processing region to etch the low-kmaterial from the narrow gap while retaining the low-k material in thewide gap; and forming a non-conformal layer of dielectric on thepatterned substrate, wherein dielectric formed on each copper line growand join together to trap an air gap in the narrow gap while the widegap remains filled with low-k dielectric material.